Chelsea had their attack to thank for their place in the FA Cup fourth round.

Normal service was resumed as two-goal Pedro, Michy Batshuayi and Willian helped the ten-man Blues put their midweek defeat against Tottenham behind them to ease past Peterborough, 4-1 .

But normal for the Stamford Bridge side these days increasingly looks like it no longer includes John Terry .

Stalwart Terry was back in the team, making his first start since October. But the 36-year-old had a miserable return, looked shaky throughout and this uncomfortable comeback was capped when he was sent off in the second half for a clumsy challenge on Lee Angol.

Branislav Ivanovic, 32, also struggled as a right wing-back and at centre-back against the plucky League One visitors.

Kurt Zouma could at least be forgiven on the couple of occasions he looked rusty, as he was making his first appearance for 11 months after a serious knee injury.

Having shuffled his pack to assess his alternatives, there was little here to convince boss Antonio Conte to change his first-choice defensive line-up any time soon, despite his post-match praise.

With the Blues looking shaky at the back, and given more of a test by Peterborough than many of their Premier League rivals in the last few months, it was down to Pedro, Willian and Batshuayi to book their spot in the next round.

Pedro and fellow scorer Willian were excellent. Batshuayi grabbed Chelsea’s other goal but was also frustratingly wasteful as he failed to make the most of his big chance to impress Conte in a rare start.

Peterborough took a leaf out of Tottenham’s book in Chelsea’s first game since their aura of invincibility was shattered by their London rivals on Wednesday night.

He had vowed to go after the Blues, boss Grant McCann was true to his word.

They boldly matched up the hosts’ three-man attack with just a trio of defenders. And they weren’t overawed on the ball either, raiding forward as they ambitiously went toe-to-toe with the Premier League leaders.

The League One side’s much-talked about young talents Marcus Maddison and Leonardo Da Silva Lopes looked comfortable on the big Stamford Bridge stage.

And Chelsea’s uncertainty at the back – Terry, Zouma and Ivanovic were all guilty of giving the ball away early on – only gave Posh further encouragement.

What they lacked, until it was too late, was a ruthlessness in front of goal.

Batshuayi doubled Chelsea's lead just before halftime... (Image: Getty)

...and Willian got their third early in the second half (Image: Action Images via Reuters)

Angol and Maddison both saw their names up in lights but their composure deserted them at the crucial moment. Defender Ryan Tafazolli also sent a free header wide.

To cause an upset, they are the sort of chances that simply have to be taken.

As well as predicting Chelsea could be vulnerable, McCann had also warned about their threat on the break.

But it is one thing knowing about it, and another trying to stop it.

Peterborough couldn’t, and paid the price twice before half-time as their determination to play got them in trouble.

Tom Nichols gave the away fans something to remember with their consolation goal (Image: Reuters)

Pedro showed them how it is done, keeping his cool to smash Chelsea ahead after they were gifted possession by Michael Smith’s misplaced pass.

The goal-scorer also hit the bar after another lightning counter, before Batshuayi finished off a four-versus-two breakaway to make it 2-0.

Luke McGee, who delayed Chelsea opening the scoring with saves from Gary Cahill and Terry, denied Willian a third with his feet. But the Brazilian beat the on-loan Spurs keeper in the 52nd minute, after being teed up by Pedro.

Terry’s dismissal and Tom Nichols’ souvenir goal with 20 minutes gave the visitors a glimmer of hope, but Pedro curled in his second five minutes later to kill Peterborough off once and for all.